This invention relates in general to methods and apparatus for aerating bodies of water and in particular, to methods and apparatus for agitating sludge.
There are various methods and apparatus which are intended for mixing, influencing and aerating bodies of water (or other liquids) such as lagoons, sludge basins, ponds and reservoirs. Often the apparatus are designed so as to float on the surface of the body of water and, in certain instances, the apparatus may be intended as a means of purification of waste water.
The following list of patents disclose various designs and features of such aerating apparatus:
______________________________________ Patent No. Patentee Issue Date ______________________________________ 3,709,470 Auler et al. 1/09/73 3,653,641 Eron 4/04/72 3,548,770 Boutros 12/22/70 3,320,160 Welles, Jr. et al. 5/16/67 3,589,997 Grutsch et al. 6/29/71 3,794,303 Hirshon 2/26/74 ______________________________________
Auler et al. discloses a floating apparatus for aeration which includes floating means for supporting the apparatus while not significantly reducing the efficiency of the surface flow created by the apparatus.
Eron discloses a floating liquid aerator and water treatment device adapted for use in aerating and the chemical treatment of polluted water. Surface water is introduced into the device and is radially sprayed creating droplets which increase aeration. The aerated water is returned to the bottom of the body of water by means of hydrostatic water pressure.
Boutros discloses an aerator platform having a plurality of pontoons which are angularly adjustable. There is no disclosure within this patent pertaining to the type or style of aerating device which is to be employed with the aerator platform.
Welles, Jr. et al. discloses a method and apparatus for aerating a large body of water using a relatively small number of floating aeration units. Rather than employ stationary aerating units, the disclosed invention provides cable and pulley means to move the aeration unit reciprocally across the length of the particular body of water. Although different styles of aeration units may be employed with this cable and pulley arrangement, the aeration units which are disclosed are conventional and are intended primarily for water or other low viscosity fluids by the nature of their design.
Grutsch et al. discloses a method for purifying waste water wherein a plurality of lagoons are employed for various treatment stages and an aerating apparatus moves across the surface of each lagoon. The aerating apparatus may be, for example, a paddle wheel type of device which aerates the lower strata of the lagoons and keeps the sludge stirred up and keeps the sludge in a state of suspension with the water. The blades of the paddle wheel design shown in Grutsch et al. are of such a length so as to extend only a short distance below the surface of the water and the sludge deposit depth comprises an extremely minor proportion of the overall lagoon depth.
Hirshon discloses a method and apparatus for aerating bodies of water wherein water is introduced into the aerator by an inlet duct. At the open end of the inlet duct is a bubble tube which receives air under pressure from a suitable source and bubbles this air into the water. These air bubbles both aerate water and raise it above its normal level, thereby providing a sufficient head to force the aerated water out through a return duct. Although the entire apparatus is supported by floats, its movement across the body of water is restricted by being tied to a buoy and the inlet duct is of a fixed length and wound not be able to accommodate different lagoon depths.
Although each of these various apparatus may in fact, in selected instances, be of value to solve a particular problem or effect a desired result, they each have certain disadvantages and shortcomings relative to the following objective.
Waste water treatment facilities typically use lagoons in which sludge deposits collect. Eventually, these lagoons become filled with the sludge and the sludge must be pumped out and transferred to a more distant site so that the lagoon which is adjacent the treatment facility can continue to be used. Sludge deposits in such waste water treatment facility lagoons may accumulate to a depth of fifteen or sixteen feet and often this leaves only three to four feet of water on the surface above the sludge. The solid content of the sludge which is below this surface water increases proportionately with depth. Although the sludge which is adjacent the surface water may only have a solids content of from 6% to 8%, the sludge at the bottom of the lagoon may have a solids content of as high as 20%. In order to be pumpable, it is generally recognized that the solids content should be something less than 20% and it is felt that a preferable maximum value is between 16% and 18%. Of course, additional water could be added to the sludge in order to reduce the percent of solids content, but this procedure would increase the total volume and weight of what must be pumped out of the lagoon and would only tend to increase and compound the task that lies ahead. Furthermore, the various solids which comprise such sludge deposits are often thixotropic in nature and may coagulate into a single gelled mass, if not frequently stirred or agitated. Consequently, unless the sludge-filled lagoon has been frequently agitated during the accumulation of the sludge deposit, conventional aerating and agitating devices are not able to disrupt the gelled mass of sludge in order to stir and agitate the sludge. Such agitation is necessary in order to mix the surface water with the sludge so that the resulting mixture will be thinned to a degree such that its viscosity will be low enough to be pumpable by conventional fluid pumps. Aerating and agitating devices which intake water are unable to handle the gelled mass of sludge, and those devices which generate a stream of air are only effective in the localized area where the outlet nozzles are located. Inasmuch as this localized area may only be several inches in diameter, it is necessary to be able to move the outlet nozzles vertically throughout the gelled mass of sludge and to move from one position to another across the lagoon as localized areas are aerated and mixed. None of the disclosed devices satisfy these various requirements.